This invention relates to acoustic, sound-absorbing nacelles or casings which are applied for aircraft jet-engines, fans, or compressors, etc. and more particularly to an active acoustic wall applicable for ordinary sound arresters or sound-absorbing room walls.
There are illustrated in FIGS. 20 to 23 structural views of conventional acoustic walls. In FIG. 20, 41 is a surface porous material, 42 are air layers, 43 are partition plates, and 44 is a back wall as a fixing section. An acoustic wall is constituted, as shown, by the porous material 41 provided on a surface thereof, a plurality of the partition plates 43 dividing an interior thereof to provide the air layers 42, and the back wall 44 onto which these elements are fixed.
Examples for acoustic walls are given, i.e., no porous material are used in the surface in FIG. 21, a perforated plate 52 having a plurality of perforations 52a is employed instead of the surface porous material 41 in FIG. 22, and a sound-absorbent material 45 is filled in place of the air layers 42 in FIG. 23.